The battle may be entirely legendary, due to the scarcity of
records from this early date in Roman history. According to Livy the fight was waged against the
Latins, with help from Tarquinius
Superbus, the former Etruscan king of Rome. Lake Regillus, the relic of
a volcanic crater, was dried in the IV century BC: it was located
not far from Frascati and
the ruins of Tusculum, in
Prataporci site, east to Rome (15 miles from Servian wall).

Aulus Postumius Albus
was dictator
for the year and Titus Aebutius Elva was master of the horse. Octavius
Mamilius, Tarquinius, and his son Sextus led the Latins; the
presence of the Tarquinii caused the Romans to fight more
passionately than in any previous battle. Tarquinius was injured at
the beginning of the battle when he attacked Postumius; Aebutius
meanwhile attacked Mamilius, but was injured in the arm, while
Mamilius suffered a minor wound to the chest. Tarquinius' troops,
made up of exiled Romans, began to push the Romans back, and Marcus
Valerius Volusus (consul 505 BC) was killed by a spear when he
tried to attack Sextus. Postumius then brought fresh troops from
his own bodyguard into the battle. Mamilius was killed in the
ensuing fight by Titus Herminius, who was subsequently killed by a
javelin. Postumius ordered the equites to dismount
and attack on foot, and soon the Latins were forced to retreat. The
Latin camp was also captured. Postumius and Aebutius returned to
Rome in triumph.[4]

A popular Roman legend had the Dioscuri (Castor and
Pollux) helping in the victory, transfigured as two young horsemen,
and Postumius ordered a temple built to them in the
Roman Forum, in the
place in which they were watering their horses.